If some of the MBHS kids know something more than they're saying about that night/early morning, I can see why they would clam up. If Natalee had "let her hair down" and was behaving out of character for her, they wouldn't want to rat on her. If that were true and others in the group indulged in a last night burst of fun and freedom also, they are hardly going to single Natalee out for criticism.
Absolutely not! She is mysteriously missing and, tragically, could be dead.
While the question has occurred to me, as far as I know, there is NO EVIDENCE THAT THE MBHS GRADS HAVE HIDDEN ANYTHING THEY KNOW.
I agree. The MB kids are being asked questions that they cannot answer. Because of that it makes them look guilty of something to some people. I can understand that to a degree. But I don't think any of them had anything to do with her disappearance. They are probably feeling very bad about this and wish they had paid more attention to what was going on. They can't do anything about that now.